Conformational dynamics and temperature dependence of photoinduced electron transfer within self-assembled coproporphyrin:cytochrome c complexes

Adsorption Properties and Electron-transfer Rates of a Redox Probe at Different Interfaces of an Immunoassay Assembled on an Electro-active Photonic Platform

Physical and chemical properties of a redox protein adsorbed to different interfaces of a multilayer immunoassay assembly were studied using a single-mode, electro-active, integrated optical waveguide (SM-EA-IOW) platform. For each interface of the immunoassay assembly (indium tin oxide, 3-aminopropyl triethoxysilane, recombinant protein G, antibody, and bovine serum albumin) the surface density, the adsorption kinetics, and the electron-transfer rate of bound species of the redox-active cytochrome c (Cyt-C) protein were accurately quantified at very low surface concentrations of redox species (from 0.4 to 4% of a full monolayer) using a highly sensitive optical impedance spectroscopy (OIS) technique based on measurements obtained with the SM-EA-IOW platform. The technique is shown here to provide quantitative insights into an important immunoassay assembly for characterization and understanding of the mechanisms of electron transfer rate, the affinity strength of molecular binding, and the associated bio-selectivity. Such methodology and acquired knowledge are crucial for the development of novel and advanced immuno-biosensors.

Electronic structure and bridge geometric distortion in push–pull imine-bridged triads. A theoretical study

Intramolecular electron transfer (IET) in imine-bridged triads is studied by analyzing electric charge distribution and ferrocene and bridge distortion parameters.

Intramolecular Path Determination of Active Electrons on Push-Pull Oligocarbazole Dyes-Sensitized Solar Cells

Several push‐pull oligocarbazole dye‐sensitizers have been studied using theoretical methods in order to better understand the relationship between structural electronic or optical properties and intramolecular path of active electrons during the ionization and injection processes. DFT/TD‐DFT calculations were performed on a series of five dye sensitizers. They differ by the presence of electron donating group (EDG) by inductive effect (noted+I) or electron releasing group (ERG) by mesomeric effect (noted+M) or electron withdrawing group by inductive effect (noted‐I) on the pushed part of the dyes studied. Our work focused on the internal distribution of electrons in the different parts of dye that are the push/pull moieties and the π‐bridge. The study concerned the ground state, the electronic transition process and the excited state. In each situation, the fragment acting in the ionization or transition phenomena were identified. In the ground state, the electrons of the push part appear to be the least bound because they have the highest probabilities of ionization. In the excited state, the ionized atoms are essentially positioned in the pushing part and some neighboring atoms of the bridge. In the electronic transition, the active atoms are located in the π‐conjugated part but only on the side adjacent to the acceptor group. To arrive to this conclusion, we optimized the structures of the five dyes in their ground and excited states. We calculated the atomic charges, the wavelengths and intensities of electronic transitions in the visible domain, the reorganization energies as well as the oxidation potential. It appears that +M donor ligands improve the performance of a dye because the great distribution of atoms to be ionized in the push parts.

Biophysical characterization of the interaction of human albumin with an anionic porphyrin

The manuscript describes the characterization of the interaction between meso-tetrakis(p-sulfonatophenyl)porphyrin (TSPP) and human serum albumin (HSA). TSPP is a candidate for the photosensitization of structural and functional changes in proteins while HSA provides both an excellent protein model and binding and functional characteristics that could be explored in future applications of the approach. A combination of optical spectroscopic techniques (e.g., fluorescence spectroscopy, fluorescence lifetime, circular dichroism, etc.) and computational docking simulations were applied to better characterize the TSPP/HSA interaction. Recent advances have revealed that the complex formed by TSPP and HSA has become potentially relevant to biomedical applications, biomaterials research and protein photosensitized engineering. The study has determined a likely location of the binding site that places TSPP at a site that overlaps partially with the low affinity site of ibuprofen and places one of the SO3− groups of the ligand in proximity of the Trp214 residue in HSA. The characterization will enable future studies aimed at photosensitizing non-native functions of HSA for biomedical and biomaterial applications.

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A novel protocol involving extensive dialysis and centrifugation eliminated aggregated protoporphyrins from the solution.

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Reliable FRET between Trp214 and the porphyrin ligands was established.

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FRET and docking simulations converge to a model consistent with experimental X-ray data.

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Photosensitization mediated by the porphyrin ligands prompts localized conformational changes in HSA.

Quantitatively mapping cellular viscosity with detailed organelle information via a designed PET fluorescent probe

Viscosity is a fundamental physical parameter that influences diffusion in biological processes. The distribution of intracellular viscosity is highly heterogeneous, and it is challenging to obtain a full map of cellular viscosity with detailed organelle information. In this work, we report 1 as the first fluorescent viscosity probe which is able to quantitatively map cellular viscosity with detailed organelle information based on the PET mechanism. This probe exhibited a significant ratiometric fluorescence intensity enhancement as solvent viscosity increases. The emission intensity increase was attributed to combined effects of the inhibition of PET due to restricted conformational access (favorable for FRET, but not for PET), and the decreased PET efficiency caused by viscosity-dependent twisted intramolecular charge transfer (TICT). A full map of subcellular viscosity was successfully constructed via fluorescent ratiometric detection and fluorescence lifetime imaging; it was found that lysosomal regions in a cell possess the highest viscosity, followed by mitochondrial regions.

Interpretation of fluorescence decay kinetics in 3-methylbenzimidazolyl(5'-5')guanosine dinucleotides: exponential dependence on the number of phosphates in the polyphosphate bridge

The number of phosphate groups in the 5',5'-polyphosphate bridge of mRNA-cap dinucleotide analogues affects kinetics of long-range electron transfer (ET) responsible for 3-methylbenzimidazole (m(3)B) fluorescence quenching in model dinucleotides. For instance, 3-methylbenzimidazolyl(5'-5')guanosine dinucleotides (m(3)Bp( n )G, n = 2, 3, 4) having m(3)B donor, 5'-5' polyphosphate bridge, and guanine (G) acceptor, exhibit exponential dependence of the ET rate on the number of phosphates, i.e. donor-acceptor distance. Involvement of the 5'-5' polyphosphate bridge in the ET is strongly indicated by lack of m(3)B-G stacking effect on the exponential factor, which is the same at 20 degrees C, where m(3)B-G intramolecular stacking dominates, as that at 75 degrees C where stacking-unstacking equilibrium is shifted in favour of the unstacked structure.

Computational Prediction and Experimental Evaluation of a Photoinduced Electron-Transfer Sensor

An approach is presented for the design of photoinduced electron-transfer-based sensors. The approach relies on the computational and theoretical prediction of electron-transfer kinetics based on Rehm-Weller and Marcus theories. The approach allows evaluation of the photophysical behavior of a prototype fluorescent probe/sensor prior to the synthesis of the molecule. As a proof of concept, a prototype sensor for divalent metal ions is evaluated computationally, synthesized, and then analyzed spectroscopically for its fluorescence response to zinc. Calculations predicted that the system would show a competition between electron transfer and fluorescence in the free state. In the zinc-bound state, the compound was predicted to be more highly fluorescent, due to the inhibition of electron transfer. Both predictions were confirmed experimentally. A nonzero fluorescence signal was observed in the absence of zinc and an enhancement was observed in the presence of zinc. Specifically, a 56-fold enhancement was observed over a 10-fold increase in zinc concentration.

Electron-transfer mechanism of the triplet state quenching of aluminium tetrasulfonated phthalocyanine by cytochrome c

The mechanism of electron-transfer from aluminium tetrasulfonated phthalocyanine triplet state to cytochrome c was investigated in this work. This reaction successfully quenches the dye triplet state due to the formation of complexes between the solute and the protein at the active site. The electron-transfer rate constant is around 3x10(7) s(-1), and is in accordance with previous results for the singlet excited state quenching [C.A.T. Laia, S.M.B. Costa, D. Phillips, A. Beeby. Electron-transfer kinetics in sulfonated aluminum phthalocyanines/cytochrome c complexes, J. Phys. Chem. B 108 (2004) 7506-7514.] in the framework of the Marcus theory, with a reorganization energy equal to 0.94 eV. The complex formation is diffusion controlled, but heterogeneities of the protein surface charge distribution lead to quenching rate constants smaller than predicted on a hard-spheres model with electrostatic interactions. Also the binding equilibrium constant is strongly affected by this phenomenon. Ionic strength plays an important role on the complex formation, but its effect on the unimolecular electron-transfer rate constant is negligible within experimental error.

Electrostatics of Cytochrome-c assemblies

Electrostatic potentials along with computational mutagenesis are used to obtain atomic level insights into Cytochrome-c in order to design efficient bionanosensors. The electrostatic properties of wild type and mutant Cytochrome-c are examined in the context of their assembly, i.e. are examined in the absence and presence of neighboring molecules from the assembly. An intense increase in the positive potential ensues when the neighboring molecules are taken into account. This suggests that in the extrapolation of electric field effects upon the design of assemblies, considering the properties of only the central molecule may not be sufficient. Additionally, the influence of the uncharged residues becomes quite diminished when the molecule is considered in an assembly. This could pave the way for making mutants that might be more soluble in different media used in the construction of devices. [Figure: see text]. The electrostatic potential, calculated using the program DELPHI mapped on to the surface of Cytochrome-c when it is considered by itself (in the left column) and in the presence of the electrostatic field generated by the presence of the surrounding 4 molecules on the right. The potentials range from -10kT in red to +10kT in blue. The central figure shows the regions that have been mutated to positively charged residues by placing a unit positive charge at the terminal atom of the respective side chain. The figures range from the wild type in the first row, followed by the Gln12, Asn70, Asp50, Glu90 and Ala83 mutants.

Gated Electron Transfer as a Probe of the Configurational Dynamics of Peptide−Protein Complexes

Gated electron-transfer measurements are used to probe the configurational dynamics of complexes formed between small metallopeptides and cytochrome c. The results show that that an apparently subtle chemical alteration of the metallopeptide produces significant changes to the dynamics of the peptide-protein complex.